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Vol. 18 (2015 year), No. 2
The paper presents a statistical analysis of chemical compositions sampling of rocks from contact aureole of the alkaline-ultrabasic carbonatitic massif Ozernaya Varaka by the principal component method. Three main factors having the greatest influence on the rocks composition alteration have been identified. All the three are associated with metasomatic processes occurring in the contact aureole at various stages of the complex formation – foidolitic, carbonatitic and postcarbonatitic. Each factor has received its mineralogical and geochemical interpretation, the results of which allowed to confirm a number of conclusions made earlier, and significantly supplement them
(in Russian, стр.10, fig. 2, tables. 1, ref 11, Adobe PDF, Adobe PDF 0 Kb)
Vol. 20 (2017 year), No. 1, DOI: 10.21443/1560-9278-2017-20-1/1
Fomina E. N., Kozlov E. N., Lokhova O. V., Lokhov K. I.
Graphite as an indicator of contact influence of Western Keivy
alkaline granite intrusion, the Kola Peninsula
The results of complex petro-mineragraphic, Raman and isotope-geochemical study of three types of graphitebearing rocks circulated at different distances from the alkaline granites: (1) kyanite schists of Bolshiye Keivy, sampled at a considerable distance from a contact with alkaline granites; (2) sillimanite schists, sampled close to the contact, and (3) silexites, located in the inner part of the alkaline granite massif Western Keivy have been presented. Five morphogenetic types of graphite have been revealed in the rocks under consideration: finegrained Gr-1, intergranular Gr-2, nest-shaped Gr-3, vein Gr-4 and spherulitic Gr-5. Current study demonstrates that these five types of graphite distinctly vary not only in morphology, but also in temperature of crystallization, as determined by RSCM-Raman geothermometer, and in carbon isotope composition. The most likely source for the anomalous "light" graphite Gr-1 and Gr-2 [?13C(PDB) = ?43…?45 ‰] from kyanite schists is a watermethane fluid originating from sedimentary rocks with organic compounds. The carbon of graphite Gr-5 of the silexites selected at the inner part of alkaline granite massif Western Keivy, on the contrary, proved to be most "heavy" [?13C(PDB) = ?8 ‰], which indicates its origin from the lower crustal or mantle carbon dioxide fluid. Thus, carbon extracted into the rocks of Keivy structure from at least two contrasting isotope sources. Graphite Gr-3, that makes up the bulk of graphite of exocontact sillimanite schists, is also isotopically light, but not anomalously [?13C(PDB) = ?17…?28 ‰]. The crystallization temperature of the given graphite (435?520 ?C), and its structural relationships with other minerals of the rock evidence of its synmetamorphic origin. The presence of veinlets of isotopically heavy [?13C(PDB) = ?10 ‰…?11 ‰] high-temperature (570?670 ?C) graphite intersecting minerals of the metamorphic paragenesis (including Gr-3) indicates that the introduction of the granites occurred into the previously metamorphosed strata and was accompanied by thermal and fluid influence on these strata.
(in Russian, стр.11, fig. 7, tables. 0, ref 17, Adobe PDF, Adobe PDF 0 Kb)
Vol. 21 (2018 year), No. 1, DOI: 10.21443/1560-9278-2018-21-1
Kozlov E. N., Fomina E. N., Sidorov M. Yu., Kirkin V. V.
Genesis of apocarbonatitic titanium metasomatites of the Petyayan-vara rare-earth occurrence (Vuoriyarvi, the Kola Region)
The objects of the study are apocarbonatitic titanium metasomatites ("titanium carbonatites") associated with the rare earth carbonatites of the Petyayan-Vara area of the Vuoriyarvi complex (the Kola region). In this paper, the following mechanism for the formation of these rocks has been substantiated based on the agreed results of mineralogical and geochemical studies. Prior to the onset of carbonatite genesis, a fluorine-enriched fluid phase originated in the lower horizons of the complex passed along the deep-permeating fracture system of several hundred meters length up to the level of the modern erosion surface. It transported Al, Fe2+, Mg, Ti, P into the pyroxenites and Si, Ca and Na out of them, as a result of which the pyroxenites were transformed into giant-grained phlogopite rocks – glimmerites. The most probable source of this fluid is alkaline aluminosilicate magma. Then carbonate melts intruded along the same fractures. In the course of carbonatite genesis, F-fluid caused a local migration of K, Al, Si, Fe, P, Ti, Nb, Ta, Zr, Hf and HREE out of glimmerites into igneous dolomite carbonatites, which led to the formation of apocarbonatitic titanium metasomatites. They represent several paragenetic associations superimposed on each other, the mineral composition and the formation sequence of which correspond to the metasomatic column zones directly observed within the contact "carbonatite – altered pyroxenite". The separation of HFSE and REE is controlled by the same metasomatic column: Ti, Nb and Ta were accumulated in titanium carbonatites, i. e. in associations of the frontal and intermediate zones, and Zr, Hf and HREE – in apatitized fields corresponding to the rear zone of the column. Accordingly, the fractionation of these elements occurred due to the "fluid – rock" interaction. Subsequently, the same long-lived fractures served as a channel for REE-Sr-Ba-S fluids, but the recrystallization caused by K-Al-Si-Ti-F-metasomatism made titanium carbonatites dense and fine-grained in texture, what, in most cases, "protected" these rocks from the influences of later processes.
(in Russian, стр.13, fig. 5, tables. 0, ref 26, adobe PDF, adobe PDF 0 Kb)
Vol. 24 (2021 year), No. 1, DOI: 10.21443/1560-9278-2021-24-1
M. Yu. Sidorov, Kozlov E. N., Fomina E. N.
Geology, petrography and mineralogy of explosive breccias of Sallanlatva, Kola Region
The Sallanlatva massif belongs to the group of Paleozoic alkaline-ultrabasic complexes wide spread in the Kola Region (the northwestern part of the Fennoscandian Shield). In the central part of this massif, the host ijolite and urtites contain calcite, ankerite, ankerite-dolomite and siderite carbonatites. The explosive processes that led to the formation of carbonatite breccias in the calcite and ankerite-dolomite carbonatites occurred in Sallanlatva massife in the last stages of the carbonatite magmatism. There are two types of explosive carbonatite breccias in the Sallanlatva massif: (1) glimmerite-calciocarbonatite breccias, and (2) siderite-dolomite breccias. Analysis of the mineral composition of fragments and matrix and the shape of fragments in breccias has shown that the first material to intrude into the host calcite and ankerite-dolomite carbonatites was calcite melt. After that, dolomite melt penetrated through the fracture zones, which resulted in the formation of siderite-dolomite breccias. The differences in the mineral composition of the breccia matrix suggest that the residual carbonatite melts originate from separate magma chambers. The chamber with calcite melt was located at great depth, and some captured glimmerite fragments were abraded during the melt upwelling. Silicate-dolomite melts lifted from a shallower depth; the captured fragments of siderite carbonatites retained their angular shape. Late hydrothermal processes yielded veins and caverns with Ba-Sr-P-S-Ti-REE mineralization in the breccias and host rocks.
(in Russian, стр.9, fig. 4, tables. 1, ref 21, AdobePDF, AdobePDF 0 Kb)